The transportation and introduction of non-indigenous species in ship ballast water has created substantial economic and environmental impact throughout the world. Ballast water transport of alien species has been determined to be a national environmental preservation issue of the highest priority. Zebra mussels in the Great Lakes, toxic dinoflagellates in Australia, stinging jellyfish along the California coast, and numerous fish and invertebrate species in Hawaii have all been transported into new predator-free habitats via ship ballast water. These introductions have caused broad environmental impact, have cost millions of dollars in remedial actions, and have focused government regulators on the development of controls that will have serious ramifications to both commercial and military shipping.
To address this problem, the United States Congress passed the Non-indigenous Aquatic Nuisance Prevention and Control Act of 1990, and further directed the National Research Council to prepare a report on the problem. That report, Stemming the Tide (Natl. Acad. Sci., 1996), lists several potential control mechanisms and discusses the merits and shortcomings of each. For example, while filtration of the ballast water may seem to be a logical solution, the volume and rate of filtration (to 25,000 m3/hr), coupled with occasional heavy silt loads, make this option unacceptable. Other methods, including the use of biocides, ozonation, ultraviolet treatment, deoxygenation, magnetic fields and sonication, have been tested, each with operational or economic shortcomings.
Tests involving sonication were effective at killing the veliger (larval) stage of the zebra mussel under well-defined conditions. Ultrasonics have been shown to be effective in destroying micro-organisms, including bacteria and fungi, at various frequencies and intensities. High intensity sound bursts created by underwater electrical arcs have been shown to be effective against some fouling problems encountered in electrical plant cooling water intake systems. However, problems with uniform sound wave penetration and energy loss at various points within the sound field limit the use of these techniques. These problems are largely a function of the method of sound production from a limited number of transducers and sound energy attenuation away from the nodes.
Needs exist for control of unwanted biological material in transportation and relocation of large water volumes.
The invention solves the problem by providing a new ship ultrasonic ballast water treatment system to eliminate the transfer of non-indigenous marine species between ports of call.
The invention provides a new concept in underwater sound generation that effectively eliminates problems of sound energy attenuation and xe2x80x9cblindxe2x80x9d spots within the sound field. A continuous piezoelectric transducer, either polyvinylidene fluoride or piezoceramic, is used to generate a broad range of sound wavelengths and energy levels within a pipe. Further, use of this technology provides an ultrasonic system with great potential. Importantly, the correct geometric configuration produces spatially-controllable, continuous, constructive-interference zones to enhance the destructive force generated in the pipe lumen, and to provide the complete destruction of micro-organisms, algae, diatoms, veligers and fish larvae and other plankton.
The insides of the in-take and out-take manifolds are sheathed with the piezoelectric material to create one long, continuous sound transducer tube within the pipe. This presents a complex array of high intensity sound through which all of the ballast water and entrained organisms enter or leave the ship.
When ballast water management is required aboard ships, the use of sonification to effectively sterilize ballast water is relatively easily implemented without costly shoreside facilities, nor does it require mid-ocean ballast water changes.
This same technique also provides a method to keep seawater coolant intakes on shore-based power-generation facilities, and those on board surface vessels or submarines, free of fouling organisms without the use of caustic or otherwise hazardous chemicals.
Ultrasonic ballast water treatment systems have shown variable results due to design and construction limitations. For conventional configurations, the intensity varies as a function of the distance from the source, limiting the effectiveness of the device. The use of a piezoelectric material to line a cylindrical tube offsets the problems of varied spatial intensity in discrete transducer systems and provides a continuous source of axi-symmetric ultrasonic excitation. Constructive interference, controlled by design geometry and modulation of the ultrasound frequency input, can be produced in a spatially-sweeping manner to further enhance the pressure fluctuation amplitude. Additionally, design geometry may be varied by linear section to enhance section resonance characteristics. Application of a transducer to the end of a diffuser pipe is also used to create uniform spatial intensity.
A preferred embodiment of a ballast intake and exhaust tube comprises a section of middle pipe and a diffuser pipe and a shroud connected to each end of the middle pipe. The shroud houses the end of the diffuser pipe. In a preferred embodiment, the middle pipe is connected to the diffuser pipe by quarter-inch flanges and half-inch flanges. The diffuser pipe is terminated by an end plate. This end plate stops the flow of ballast water, and allows the water to be circulated back through the piezoelectric transducer, which lines the middle and diffuser pipe, or is mounted at the end of the diffuser.
Preferably, the shroud housing the diffuser pipe comprises a cylindrical tube into which are fitted two or more seating rings. The seating rings hold the diffuser pipe in place within the shroud. Additionally, a cylindrical extension extends from the cylindrical tube of the shroud.
A preferred embodiment of a diffuser pipe comprises a section of pipe having the same diameter as the middle pipe with holes cut into one end. Additionally, a larger hole is cut into the diffuser pipe to align with the cylindrical extension of the shroud into which the diffuser pipe is placed. In a preferred embodiment, the end of the diffuser pipe into which holes are cut is terminated by an end plate.
This invention allows for uniform and controllable sound fields and symmetric interference patterns throughout the entire pipe volume.
These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the claims and the drawings.